Title: CELL MEMBRANES and TRANSPORT
1CELL MEMBRANESandTRANSPORT
2The Cell
3Cell Membrane
- All living things are surrounded by a membrane.
- A cell membrane is also known as plasma
membrane.
- Controls exchange of materials such as nutrients
and waste between cells and their environment.
- Has other important functions
- for example to enable cells to receive hormones.
4Cell Membrane
- Fluid Mosaic Model - proteins embedded in a
phospholipid bilayer.
5Fluid mosaic model
- FLUID- because individual phospholipids and
proteins can move around freely within the layer,
like its a liquid. - MOSAIC- because of the pattern produced by the
scattered protein molecules when the membrane is
viewed from above.
6Cell membranes are made of PHOSPHOLIPIDS
- HYDROPHILIC heads (water liking)-Attracted to
the water - HYDROPHOBIC tails (water fearing)-repel water
A Phospholipid
7A Phospholipid Bilayer
- Phospholipids can form
- BILAYERS
- -2 layers of phospholipids with hydrophobic tails
protected inside by the hydrophilic heads. - The PHOSPHOLIPID
- BILAYER is the basic
- structure of membranes.
8- Bilayer 2 layers of phospholipids
- The heads stay on the outside and the tails stay
on the inside.
9Cell Membrane
- Cell surface proteins
- a. Channel proteins - transport food and other
molecules into the cell and transport wastes out
of the cells. - b. Receptor proteins - gather information about
the cells surroundings. - c. Cell surface markers - identify the type of
cell, important for cell recognition.
10Movement of selected molecules across the cell
membrane
11Cell Membrane
- Permeability of the cell membrane
- 1. Semi permeable/selectively permeable - only
certain substances can pass across the membrane. - 2. Factors that determine whether a molecule can
pass through a membrane or not - a. size
- b. type
12Transport Mechanisms
- Transport Mechanisms - moving material in and out
of the cell - Concentration gradient - the difference in the
amount of a substance inside and outside of the
cell - 1. Going with the gradient-moving from high to
low concentration - 2. Going against the gradient-moving from low
to high concentration - 3. Equilibrium exists when the concentration of
molecules is the same throughout a space (inside
and outside the cell)
13Transport Mechanisms
- Two categories of transport based on
concentration gradient and the need for energy - 1. Passive transport does not require energy
- goes with the gradient.
- 2. Active transport requires energy
- goes against the gradient.
14Methods of Transport Across Membranes
- 1. Diffusion
- 2. Osmosis
- 3. Facilitated Diffusion
- 4. Active Transport
15Methods of Transport Across Membranes
- Diffusion -passive transport - no
- energy expended
- 2. Osmosis - Passive transport of water
across membrane - Facilitated Diffusion - Use of proteins to
- carry molecules or ions across
- Active Transport- requires energy to
- transport molecules against a
- concentration gradient energy is
- in the form of ATP
16Types of Transport
17Passive Transport Mechanisms Diffusion
- Movement of molecules from an area of high
concentration to an area of low concentration. - Movement from one side of a membrane to another
- Example smoke across a room, food coloring
dropped into water, oxygen in lungs
18Diffusion
Diffusion in action
19Passive Transport MechanismsOsmosis
- Diffusion of water
- Direction of osmosis-the direction of water flow
depends upon the concentration of solute and
solvent (water) - Tonicity-term used to compare 2 solutions
(usually the inside and the outside of the cell) - a. Hypotonic - less solute (more water)
- b. Hypertonic - more solute (less water)
- c. Isotonic - equal amounts of solute and water
20Passive Transport MechanismsOsmosis
- Water will flow from a hypotonic solution to a
hypertonic solution - Will water move in an isotonic solution?
- Yes, but it wont be noticeable-equilibrium is
established
21Osmosis
How Osmosis works
22Solutions
- Solutions are made of solute and a solvent
- Solvent - the liquid into which the solute is
poured and dissolved. - Solute - substance that is dissolved or put into
the solvent. - Salt and sucrose are solutes.
23Passive Transport Mechanisms
- Turgor pressure/osmotic pressure-pressure due to
water in cell. - Analogy air pressure in a tire.
- When a cell has high turgor pressure, it is
bigger and stiffer. - When a cell has low turgor pressure, it is
smaller and flimsy.
24Passive Transport Mechanisms
- Plasmolysis - wilting of a cell due to loss of
turgor pressure - Cytolysis - bursting of a cell due to an increase
in turgor pressure. - How do plant cells avoid cytolysis? Cell walls
- How do unicellular freshwater organisms avoid
bursting? Contractile vacuoles.
25Plant and Animal Cells put into various
solutions
26Passive Transport Mechanisms
27Passive Transport Mechanisms
28Passive Transport Mechanisms
- Facilitated diffusion - transport of specific
molecules across a membrane with the help of a
channel protein - An example of a molecule that is often
transported in this manner is glucose
How Facilitated Diffusion Works
29Active Transport Mechanism
- Active Transport Mechanism(requires energy in
the form of ATP) - Ex.
- Sodium-potassium pump - pumps sodium ions out and
forces potassium ions in. - Important for conducting nerve impulses and
muscle contraction. - Proton pump-transport protons through membranes
of chloroplasts and mitochondria
30Active Transport Mechanism
- Endocytosis - process of bringing larger
molecules into the cell by engulfing them. - 1. Pinocytosis liquids
- 2. Phagocytosis - solids
- amoebas eat this way
- white blood cell engulf bacteria